Python-RHSM performance improvements

The RHOS os folks were seeing performance issues in the client using the employee SKU. This pull request goes after the low hanging fruit of making the OID reading a bit more performant. Even though each tweak is small, a single call to list --available would cause 100K + calls on some of these methods so little items add up

Next up would be to be a bit smarter on how to read the oids from content sets. This could be laissez-faire initializing the content sets.